/*

 * rdgif.c

 *

 * Copyright (C) 1991-1995, Thomas G. Lane.

 * This file is part of the Independent JPEG Group's software.

 * For conditions of distribution and use, see the accompanying README file.

 *

 **************************************************************************

 * WARNING: You will need an LZW patent license from Unisys in order to   *

 * use this file legally in any commercial or shareware application.      *

 **************************************************************************

 *

 * This file contains routines to read input images in GIF format.

 *

 * These routines may need modification for non-Unix environments or

 * specialized applications.  As they stand, they assume input from

 * an ordinary stdio stream.  They further assume that reading begins

 * at the start of the file; input_init may need work if the

 * user interface has already read some data (e.g., to determine that

 * the file is indeed GIF format).

 */



/*

 * This code is loosely based on giftoppm from the PBMPLUS distribution

 * of Feb. 1991.  That file contains the following copyright notice:

 * +-------------------------------------------------------------------+

 * | Copyright 1990, David Koblas.                                     |

 * |   Permission to use, copy, modify, and distribute this software   |

 * |   and its documentation for any purpose and without fee is hereby |

 * |   granted, provided that the above copyright notice appear in all |

 * |   copies and that both that copyright notice and this permission  |

 * |   notice appear in supporting documentation.  This software is    |

 * |   provided "as is" without express or implied warranty.           |

 * +-------------------------------------------------------------------+

 *

 * We are also required to state that

 *    "The Graphics Interchange Format(c) is the Copyright property of

 *    CompuServe Incorporated. GIF(sm) is a Service Mark property of

 *    CompuServe Incorporated."

 */



#include "cdjpeg.h"		/* Common decls for cjpeg/djpeg applications */



#ifdef GIF_SUPPORTED





#define	MAXCOLORMAPSIZE	256	/* max # of colors in a GIF colormap */

#define NUMCOLORS	3	/* # of colors */

#define CM_RED		0	/* color component numbers */

#define CM_GREEN	1

#define CM_BLUE		2



#define	MAX_LZW_BITS	12	/* maximum LZW code size */

#define LZW_TABLE_SIZE	(1<<MAX_LZW_BITS) /* # of possible LZW symbols */



/* Macros for extracting header data --- note we assume chars may be signed */



#define LM_to_uint(a,b)		((((b)&0xFF) << 8) | ((a)&0xFF))



#define BitSet(byte, bit)	((byte) & (bit))

#define INTERLACE	0x40	/* mask for bit signifying interlaced image */

#define COLORMAPFLAG	0x80	/* mask for bit signifying colormap presence */



#define	ReadOK(file,buffer,len)	(JFREAD(file,buffer,len) == ((size_t) (len)))



/* LZW decompression tables look like this:

 *   symbol_head[K] = prefix symbol of any LZW symbol K (0..LZW_TABLE_SIZE-1)

 *   symbol_tail[K] = suffix byte   of any LZW symbol K (0..LZW_TABLE_SIZE-1)

 * Note that entries 0..end_code of the above tables are not used,

 * since those symbols represent raw bytes or special codes.

 *

 * The stack represents the not-yet-used expansion of the last LZW symbol.

 * In the worst case, a symbol could expand to as many bytes as there are

 * LZW symbols, so we allocate LZW_TABLE_SIZE bytes for the stack.

 * (This is conservative since that number includes the raw-byte symbols.)

 *

 * The tables are allocated from FAR heap space since they would use up

 * rather a lot of the near data space in a PC.

 */





/* Private version of data source object */



typedef struct {

  struct cjpeg_source_struct pub; /* public fields */



  j_compress_ptr cinfo;		/* back link saves passing separate parm */



  JSAMPARRAY colormap;		/* GIF colormap (converted to my format) */



  /* State for GetCode and LZWReadByte */

  char code_buf[256+4];		/* current input data block */

  int last_byte;		/* # of bytes in code_buf */

  int last_bit;			/* # of bits in code_buf */

  int cur_bit;			/* next bit index to read */

  boolean out_of_blocks;	/* TRUE if hit terminator data block */



  int input_code_size;		/* codesize given in GIF file */

  int clear_code,end_code;	/* values for Clear and End codes */



  int code_size;		/* current actual code size */

  int limit_code;		/* 2^code_size */

  int max_code;			/* first unused code value */

  boolean first_time;		/* flags first call to LZWReadByte */



  /* Private state for LZWReadByte */

  int oldcode;			/* previous LZW symbol */

  int firstcode;		/* first byte of oldcode's expansion */



  /* LZW symbol table and expansion stack */

  UINT16 FAR *symbol_head;	/* => table of prefix symbols */

  UINT8  FAR *symbol_tail;	/* => table of suffix bytes */

  UINT8  FAR *symbol_stack;	/* => stack for symbol expansions */

  UINT8  FAR *sp;		/* stack pointer */



  /* State for interlaced image processing */

  boolean is_interlaced;	/* TRUE if have interlaced image */

  jvirt_sarray_ptr interlaced_image; /* full image in interlaced order */

  JDIMENSION cur_row_number;	/* need to know actual row number */

  JDIMENSION pass2_offset;	/* # of pixel rows in pass 1 */

  JDIMENSION pass3_offset;	/* # of pixel rows in passes 1&2 */

  JDIMENSION pass4_offset;	/* # of pixel rows in passes 1,2,3 */

} gif_source_struct;



typedef gif_source_struct * gif_source_ptr;





/* Forward declarations */

METHODDEF JDIMENSION get_pixel_rows

	JPP((j_compress_ptr cinfo, cjpeg_source_ptr sinfo));

METHODDEF JDIMENSION load_interlaced_image

	JPP((j_compress_ptr cinfo, cjpeg_source_ptr sinfo));

METHODDEF JDIMENSION get_interlaced_row

	JPP((j_compress_ptr cinfo, cjpeg_source_ptr sinfo));





LOCAL int

ReadByte (gif_source_ptr sinfo)

/* Read next byte from GIF file */

{

  register FILE * infile = sinfo->pub.input_file;

  int c;



  if ((c = getc(infile)) == EOF)

    ERREXIT(sinfo->cinfo, JERR_INPUT_EOF);

  return c;

}





LOCAL int

GetDataBlock (gif_source_ptr sinfo, char *buf)

/* Read a GIF data block, which has a leading count byte */

/* A zero-length block marks the end of a data block sequence */

{

  int count;



  count = ReadByte(sinfo);

  if (count > 0) {

    if (! ReadOK(sinfo->pub.input_file, buf, count))

      ERREXIT(sinfo->cinfo, JERR_INPUT_EOF);

  }

  return count;

}





LOCAL void

SkipDataBlocks (gif_source_ptr sinfo)

/* Skip a series of data blocks, until a block terminator is found */

{

  char buf[256];



  while (GetDataBlock(sinfo, buf) > 0)

    /* skip */;

}





LOCAL void

ReInitLZW (gif_source_ptr sinfo)

/* (Re)initialize LZW state; shared code for startup and Clear processing */

{

  sinfo->code_size = sinfo->input_code_size + 1;

  sinfo->limit_code = sinfo->clear_code << 1;	/* 2^code_size */

  sinfo->max_code = sinfo->clear_code + 2;	/* first unused code value */

  sinfo->sp = sinfo->symbol_stack;		/* init stack to empty */

}





LOCAL void

InitLZWCode (gif_source_ptr sinfo)

/* Initialize for a series of LZWReadByte (and hence GetCode) calls */

{

  /* GetCode initialization */

  sinfo->last_byte = 2;		/* make safe to "recopy last two bytes" */

  sinfo->last_bit = 0;		/* nothing in the buffer */

  sinfo->cur_bit = 0;		/* force buffer load on first call */

  sinfo->out_of_blocks = FALSE;



  /* LZWReadByte initialization: */

  /* compute special code values (note that these do not change later) */

  sinfo->clear_code = 1 << sinfo->input_code_size;

  sinfo->end_code = sinfo->clear_code + 1;

  sinfo->first_time = TRUE;

  ReInitLZW(sinfo);

}





LOCAL int

GetCode (gif_source_ptr sinfo)

/* Fetch the next code_size bits from the GIF data */

/* We assume code_size is less than 16 */

{

  register INT32 accum;

  int offs, ret, count;



  while ( (sinfo->cur_bit + sinfo->code_size) > sinfo->last_bit) {

    /* Time to reload the buffer */

    if (sinfo->out_of_blocks) {

      WARNMS(sinfo->cinfo, JWRN_GIF_NOMOREDATA);

      return sinfo->end_code;	/* fake something useful */

    }

    /* preserve last two bytes of what we have -- assume code_size <= 16 */

    sinfo->code_buf[0] = sinfo->code_buf[sinfo->last_byte-2];

    sinfo->code_buf[1] = sinfo->code_buf[sinfo->last_byte-1];

    /* Load more bytes; set flag if we reach the terminator block */

    if ((count = GetDataBlock(sinfo, &sinfo->code_buf[2])) == 0) {

      sinfo->out_of_blocks = TRUE;

      WARNMS(sinfo->cinfo, JWRN_GIF_NOMOREDATA);

      return sinfo->end_code;	/* fake something useful */

    }

    /* Reset counters */

    sinfo->cur_bit = (sinfo->cur_bit - sinfo->last_bit) + 16;

    sinfo->last_byte = 2 + count;

    sinfo->last_bit = sinfo->last_byte * 8;

  }



  /* Form up next 24 bits in accum */

  offs = sinfo->cur_bit >> 3;	/* byte containing cur_bit */

#ifdef CHAR_IS_UNSIGNED

  accum = sinfo->code_buf[offs+2];

  accum <<= 8;

  accum |= sinfo->code_buf[offs+1];

  accum <<= 8;

  accum |= sinfo->code_buf[offs];

#else

  accum = sinfo->code_buf[offs+2] & 0xFF;

  accum <<= 8;

  accum |= sinfo->code_buf[offs+1] & 0xFF;

  accum <<= 8;

  accum |= sinfo->code_buf[offs] & 0xFF;

#endif



  /* Right-align cur_bit in accum, then mask off desired number of bits */

  accum >>= (sinfo->cur_bit & 7);

  ret = ((int) accum) & ((1 << sinfo->code_size) - 1);

  

  sinfo->cur_bit += sinfo->code_size;

  return ret;

}





LOCAL int

LZWReadByte (gif_source_ptr sinfo)

/* Read an LZW-compressed byte */

{

  register int code;		/* current working code */

  int incode;			/* saves actual input code */



  /* First time, just eat the expected Clear code(s) and return next code, */

  /* which is expected to be a raw byte. */

  if (sinfo->first_time) {

    sinfo->first_time = FALSE;

    code = sinfo->clear_code;	/* enables sharing code with Clear case */

  } else {



    /* If any codes are stacked from a previously read symbol, return them */

    if (sinfo->sp > sinfo->symbol_stack)

      return (int) *(-- sinfo->sp);



    /* Time to read a new symbol */

    code = GetCode(sinfo);



  }



  if (code == sinfo->clear_code) {

    /* Reinit state, swallow any extra Clear codes, and */

    /* return next code, which is expected to be a raw byte. */

    ReInitLZW(sinfo);

    do {

      code = GetCode(sinfo);

    } while (code == sinfo->clear_code);

    if (code > sinfo->clear_code) { /* make sure it is a raw byte */

      WARNMS(sinfo->cinfo, JWRN_GIF_BADDATA);

      code = 0;			/* use something valid */

    }

    /* make firstcode, oldcode valid! */

    sinfo->firstcode = sinfo->oldcode = code;

    return code;

  }



  if (code == sinfo->end_code) {

    /* Skip the rest of the image, unless GetCode already read terminator */

    if (! sinfo->out_of_blocks) {

      SkipDataBlocks(sinfo);

      sinfo->out_of_blocks = TRUE;

    }

    /* Complain that there's not enough data */

    WARNMS(sinfo->cinfo, JWRN_GIF_ENDCODE);

    /* Pad data with 0's */

    return 0;			/* fake something usable */

  }



  /* Got normal raw byte or LZW symbol */

  incode = code;		/* save for a moment */

  

  if (code >= sinfo->max_code) { /* special case for not-yet-defined symbol */

    /* code == max_code is OK; anything bigger is bad data */

    if (code > sinfo->max_code) {

      WARNMS(sinfo->cinfo, JWRN_GIF_BADDATA);

      incode = 0;		/* prevent creation of loops in symbol table */

    }

    /* this symbol will be defined as oldcode/firstcode */

    *(sinfo->sp++) = (UINT8) sinfo->firstcode;

    code = sinfo->oldcode;

  }



  /* If it's a symbol, expand it into the stack */

  while (code >= sinfo->clear_code) {

    *(sinfo->sp++) = sinfo->symbol_tail[code]; /* tail is a byte value */

    code = sinfo->symbol_head[code]; /* head is another LZW symbol */

  }

  /* At this point code just represents a raw byte */

  sinfo->firstcode = code;	/* save for possible future use */



  /* If there's room in table, */

  if ((code = sinfo->max_code) < LZW_TABLE_SIZE) {

    /* Define a new symbol = prev sym + head of this sym's expansion */

    sinfo->symbol_head[code] = sinfo->oldcode;

    sinfo->symbol_tail[code] = (UINT8) sinfo->firstcode;

    sinfo->max_code++;

    /* Is it time to increase code_size? */

    if ((sinfo->max_code >= sinfo->limit_code) &&

	(sinfo->code_size < MAX_LZW_BITS)) {

      sinfo->code_size++;

      sinfo->limit_code <<= 1;	/* keep equal to 2^code_size */

    }

  }

  

  sinfo->oldcode = incode;	/* save last input symbol for future use */

  return sinfo->firstcode;	/* return first byte of symbol's expansion */

}





LOCAL void

ReadColorMap (gif_source_ptr sinfo, int cmaplen, JSAMPARRAY cmap)

/* Read a GIF colormap */

{

  int i;



  for (i = 0; i < cmaplen; i++) {

#if BITS_IN_JSAMPLE == 8

#define UPSCALE(x)  (x)

#else

#define UPSCALE(x)  ((x) << (BITS_IN_JSAMPLE-8))

#endif

    cmap[CM_RED][i]   = (JSAMPLE) UPSCALE(ReadByte(sinfo));

    cmap[CM_GREEN][i] = (JSAMPLE) UPSCALE(ReadByte(sinfo));

    cmap[CM_BLUE][i]  = (JSAMPLE) UPSCALE(ReadByte(sinfo));

  }

}





LOCAL void

DoExtension (gif_source_ptr sinfo)

/* Process an extension block */

/* Currently we ignore 'em all */

{

  int extlabel;



  /* Read extension label byte */

  extlabel = ReadByte(sinfo);

  TRACEMS1(sinfo->cinfo, 1, JTRC_GIF_EXTENSION, extlabel);

  /* Skip the data block(s) associated with the extension */

  SkipDataBlocks(sinfo);

}





/*

 * Read the file header; return image size and component count.

 */



METHODDEF void

start_input_gif (j_compress_ptr cinfo, cjpeg_source_ptr sinfo)

{

  gif_source_ptr source = (gif_source_ptr) sinfo;

  char hdrbuf[10];		/* workspace for reading control blocks */

  unsigned int width, height;	/* image dimensions */

  int colormaplen, aspectRatio;

  int c;



  /* Allocate space to store the colormap */

  source->colormap = (*cinfo->mem->alloc_sarray)

    ((j_common_ptr) cinfo, JPOOL_IMAGE,

     (JDIMENSION) MAXCOLORMAPSIZE, (JDIMENSION) NUMCOLORS);



  /* Read and verify GIF Header */

  if (! ReadOK(source->pub.input_file, hdrbuf, 6))

    ERREXIT(cinfo, JERR_GIF_NOT);

  if (hdrbuf[0] != 'G' || hdrbuf[1] != 'I' || hdrbuf[2] != 'F')

    ERREXIT(cinfo, JERR_GIF_NOT);

  /* Check for expected version numbers.

   * If unknown version, give warning and try to process anyway;

   * this is per recommendation in GIF89a standard.

   */

  if ((hdrbuf[3] != '8' || hdrbuf[4] != '7' || hdrbuf[5] != 'a') &&

      (hdrbuf[3] != '8' || hdrbuf[4] != '9' || hdrbuf[5] != 'a'))

    TRACEMS3(cinfo, 1, JTRC_GIF_BADVERSION, hdrbuf[3], hdrbuf[4], hdrbuf[5]);



  /* Read and decipher Logical Screen Descriptor */

  if (! ReadOK(source->pub.input_file, hdrbuf, 7))

    ERREXIT(cinfo, JERR_INPUT_EOF);

  width = LM_to_uint(hdrbuf[0],hdrbuf[1]);

  height = LM_to_uint(hdrbuf[2],hdrbuf[3]);

  colormaplen = 2 << (hdrbuf[4] & 0x07);

  /* we ignore the color resolution, sort flag, and background color index */

  aspectRatio = hdrbuf[6] & 0xFF;

  if (aspectRatio != 0 && aspectRatio != 49)

    TRACEMS(cinfo, 1, JTRC_GIF_NONSQUARE);



  /* Read global colormap if header indicates it is present */

  if (BitSet(hdrbuf[4], COLORMAPFLAG))

    ReadColorMap(source, colormaplen, source->colormap);



  /* Scan until we reach start of desired image.

   * We don't currently support skipping images, but could add it easily.

   */

  for (;;) {

    c = ReadByte(source);



    if (c == ';')		/* GIF terminator?? */

      ERREXIT(cinfo, JERR_GIF_IMAGENOTFOUND);



    if (c == '!') {		/* Extension */

      DoExtension(source);

      continue;

    }

    

    if (c != ',') {		/* Not an image separator? */

      WARNMS1(cinfo, JWRN_GIF_CHAR, c);

      continue;

    }



    /* Read and decipher Local Image Descriptor */

    if (! ReadOK(source->pub.input_file, hdrbuf, 9))

      ERREXIT(cinfo, JERR_INPUT_EOF);

    /* we ignore top/left position info, also sort flag */

    width = LM_to_uint(hdrbuf[4],hdrbuf[5]);

    height = LM_to_uint(hdrbuf[6],hdrbuf[7]);

    source->is_interlaced = BitSet(hdrbuf[8], INTERLACE);



    /* Read local colormap if header indicates it is present */

    /* Note: if we wanted to support skipping images, */

    /* we'd need to skip rather than read colormap for ignored images */

    if (BitSet(hdrbuf[8], COLORMAPFLAG)) {

      colormaplen = 2 << (hdrbuf[8] & 0x07);

      ReadColorMap(source, colormaplen, source->colormap);

    }



    source->input_code_size = ReadByte(source); /* get min-code-size byte */

    if (source->input_code_size < 2 || source->input_code_size >= MAX_LZW_BITS)

      ERREXIT1(cinfo, JERR_GIF_CODESIZE, source->input_code_size);



    /* Reached desired image, so break out of loop */

    /* If we wanted to skip this image, */

    /* we'd call SkipDataBlocks and then continue the loop */

    break;

  }



  /* Prepare to read selected image: first initialize LZW decompressor */

  source->symbol_head = (UINT16 FAR *)

    (*cinfo->mem->alloc_large) ((j_common_ptr) cinfo, JPOOL_IMAGE,

				LZW_TABLE_SIZE * SIZEOF(UINT16));

  source->symbol_tail = (UINT8 FAR *)

    (*cinfo->mem->alloc_large) ((j_common_ptr) cinfo, JPOOL_IMAGE,

				LZW_TABLE_SIZE * SIZEOF(UINT8));

  source->symbol_stack = (UINT8 FAR *)

    (*cinfo->mem->alloc_large) ((j_common_ptr) cinfo, JPOOL_IMAGE,

				LZW_TABLE_SIZE * SIZEOF(UINT8));

  InitLZWCode(source);



  /*

   * If image is interlaced, we read it into a full-size sample array,

   * decompressing as we go; then get_interlaced_row selects rows from the

   * sample array in the proper order.

   */

  if (source->is_interlaced) {

    /* We request the virtual array now, but can't access it until virtual

     * arrays have been allocated.  Hence, the actual work of reading the

     * image is postponed until the first call to get_pixel_rows.

     */

    source->interlaced_image = (*cinfo->mem->request_virt_sarray)

      ((j_common_ptr) cinfo, JPOOL_IMAGE, FALSE,

       (JDIMENSION) width, (JDIMENSION) height, (JDIMENSION) 1);

    if (cinfo->progress != NULL) {

      cd_progress_ptr progress = (cd_progress_ptr) cinfo->progress;

      progress->total_extra_passes++; /* count file input as separate pass */

    }

    source->pub.get_pixel_rows = load_interlaced_image;

  } else {

    source->pub.get_pixel_rows = get_pixel_rows;

  }



  /* Create compressor input buffer. */

  source->pub.buffer = (*cinfo->mem->alloc_sarray)

    ((j_common_ptr) cinfo, JPOOL_IMAGE,

     (JDIMENSION) width * NUMCOLORS, (JDIMENSION) 1);

  source->pub.buffer_height = 1;



  /* Return info about the image. */

  cinfo->in_color_space = JCS_RGB;

  cinfo->input_components = NUMCOLORS;

  cinfo->data_precision = BITS_IN_JSAMPLE; /* we always rescale data to this */

  cinfo->image_width = width;

  cinfo->image_height = height;



  TRACEMS3(cinfo, 1, JTRC_GIF, width, height, colormaplen);

}





/*

 * Read one row of pixels.

 * This version is used for noninterlaced GIF images:

 * we read directly from the GIF file.

 */



METHODDEF JDIMENSION

get_pixel_rows (j_compress_ptr cinfo, cjpeg_source_ptr sinfo)

{

  gif_source_ptr source = (gif_source_ptr) sinfo;

  register int c;

  register JSAMPROW ptr;

  register JDIMENSION col;

  register JSAMPARRAY colormap = source->colormap;

  

  ptr = source->pub.buffer[0];

  for (col = cinfo->image_width; col > 0; col--) {

    c = LZWReadByte(source);

    *ptr++ = colormap[CM_RED][c];

    *ptr++ = colormap[CM_GREEN][c];

    *ptr++ = colormap[CM_BLUE][c];

  }

  return 1;

}





/*

 * Read one row of pixels.

 * This version is used for the first call on get_pixel_rows when

 * reading an interlaced GIF file: we read the whole image into memory.

 */



METHODDEF JDIMENSION

load_interlaced_image (j_compress_ptr cinfo, cjpeg_source_ptr sinfo)

{

  gif_source_ptr source = (gif_source_ptr) sinfo;

  JSAMPARRAY image_ptr;

  register JSAMPROW sptr;

  register JDIMENSION col;

  JDIMENSION row;

  cd_progress_ptr progress = (cd_progress_ptr) cinfo->progress;



  /* Read the interlaced image into the virtual array we've created. */

  for (row = 0; row < cinfo->image_height; row++) {

    if (progress != NULL) {

      progress->pub.pass_counter = (long) row;

      progress->pub.pass_limit = (long) cinfo->image_height;

      (*progress->pub.progress_monitor) ((j_common_ptr) cinfo);

    }

    image_ptr = (*cinfo->mem->access_virt_sarray)

      ((j_common_ptr) cinfo, source->interlaced_image,

       row, (JDIMENSION) 1, TRUE);

    sptr = image_ptr[0];

    for (col = cinfo->image_width; col > 0; col--) {

      *sptr++ = (JSAMPLE) LZWReadByte(source);

    }

  }

  if (progress != NULL)

    progress->completed_extra_passes++;



  /* Replace method pointer so subsequent calls don't come here. */

  source->pub.get_pixel_rows = get_interlaced_row;

  /* Initialize for get_interlaced_row, and perform first call on it. */

  source->cur_row_number = 0;

  source->pass2_offset = (cinfo->image_height + 7) / 8;

  source->pass3_offset = source->pass2_offset + (cinfo->image_height + 3) / 8;

  source->pass4_offset = source->pass3_offset + (cinfo->image_height + 1) / 4;



  return get_interlaced_row(cinfo, sinfo);

}





/*

 * Read one row of pixels.

 * This version is used for interlaced GIF images:

 * we read from the virtual array.

 */



METHODDEF JDIMENSION

get_interlaced_row (j_compress_ptr cinfo, cjpeg_source_ptr sinfo)

{

  gif_source_ptr source = (gif_source_ptr) sinfo;

  JSAMPARRAY image_ptr;

  register int c;

  register JSAMPROW sptr, ptr;

  register JDIMENSION col;

  register JSAMPARRAY colormap = source->colormap;

  JDIMENSION irow;



  /* Figure out which row of interlaced image is needed, and access it. */

  switch ((int) (source->cur_row_number & 7)) {

  case 0:			/* first-pass row */

    irow = source->cur_row_number >> 3;

    break;

  case 4:			/* second-pass row */

    irow = (source->cur_row_number >> 3) + source->pass2_offset;

    break;

  case 2:			/* third-pass row */

  case 6:

    irow = (source->cur_row_number >> 2) + source->pass3_offset;

    break;

  default:			/* fourth-pass row */

    irow = (source->cur_row_number >> 1) + source->pass4_offset;

    break;

  }

  image_ptr = (*cinfo->mem->access_virt_sarray)

    ((j_common_ptr) cinfo, source->interlaced_image,

     irow, (JDIMENSION) 1, FALSE);

  /* Scan the row, expand colormap, and output */

  sptr = image_ptr[0];

  ptr = source->pub.buffer[0];

  for (col = cinfo->image_width; col > 0; col--) {

    c = GETJSAMPLE(*sptr++);

    *ptr++ = colormap[CM_RED][c];

    *ptr++ = colormap[CM_GREEN][c];

    *ptr++ = colormap[CM_BLUE][c];

  }

  source->cur_row_number++;	/* for next time */

  return 1;

}





/*

 * Finish up at the end of the file.

 */



METHODDEF void

finish_input_gif (j_compress_ptr cinfo, cjpeg_source_ptr sinfo)

{

  /* no work */

}





/*

 * The module selection routine for GIF format input.

 */



GLOBAL cjpeg_source_ptr

jinit_read_gif (j_compress_ptr cinfo)

{

  gif_source_ptr source;



  /* Create module interface object */

  source = (gif_source_ptr)

      (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,

				  SIZEOF(gif_source_struct));

  source->cinfo = cinfo;	/* make back link for subroutines */

  /* Fill in method ptrs, except get_pixel_rows which start_input sets */

  source->pub.start_input = start_input_gif;

  source->pub.finish_input = finish_input_gif;



  return (cjpeg_source_ptr) source;

}



#endif /* GIF_SUPPORTED */

